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DEPARTMENT OF COMMERCE 



Technologic Papers 



OP THE 



Bureau of Standards 

S. W. STRATTON, Director 



No. 166 

LABORATORY WEARING TEST TO DETERMINE THE 

RELATIVE WEAR RESISTANCE OF SOLE 

LEATHER AT DIFFERENT DEPTHS 

THROUGHOUT THE THICKNESS 

OF A HIDE 

BY 

REEVES W. HART, Assistant Physicist 

\ ii 

Bureau of Standards 



AUGUST 21, 1920 



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LABORATORY WEARING TEST TO DETERMINE THE 
RELATIVE WEAR RESISTANCE OF SOLE LEATHER 
AT DIFFERENT DEPTHS THROUGHOUT THE THICK- 
NESS OF A HIDE 



By Reeves W. Hart 



The results given in this report are those obtained from a series 
of preliminary tests and must not be regarded as the data from 
extensive researches on this subject. They are, however, sig- 
nificant in that for each individual test of this series the same 
general tendency is shown. 

The leather used for these tests was taken from a single hide 
and so marked that the relative location of each test piece could 
be ascertained. The 18 test pieces prepared for the machine- 
wearing test were divided into 6 groups, 3 of which were tested by 
wearing with the grain side out, and 3 by subjecting the flesh side 
to the wearing action. The 6 groups were prepared as follows: 

TEST PIECES TO BE WORN ON THE GRAIN SIDE 

Gi, left the original thickness of the leather. 

Gi, made approximately two- thirds original thickness by skiving off one- 
third from the grain surface. 

63, made approximately one-third original thickness by skiving off two- 
thirds from the grain surface. 

TEST PIECES TO BE WORN ON THE FLESH SIDE 

Fi, left the original thickness of the leather. 

F2, made approximately two-thirds original thickness by skiving off one- 
third from the flesh side. 

F3, made approximately one-third original thickness by skiving off two- 
thirds from the flesh side. 

By this procedure test pieces were obtained at four different 
layers of the leather, the grain surface, a depth of one-third the 
thickness of the leather, a depth of two-thirds the thickness, and 
the flesh surface. 

Three individual tests were made on the wearing-test machine 
with a sample representing each group in every test. The length 
of the runs was varied, but all the other conditions of the tests 
were kept as nearly constant as possible. 

182085°— 20 , 



4 Technologic Papers of the Bureau of Standards 

The results cf each of the three individual tests and also an 
average result of all of them are shown in the accompanying 
graphs. These graphs (Fig. i) show the relative loss in weight of 
each sample as compared to the loss in weight of the sample Gi, 
which was chosen as the basis for comparison. The arrangement 
of these graphs was based on the actual thickness of the test 
pieces. In each case there is a striking similarity between the 
results of the runs. From these data the outside surfaces of the 
leather appear to have much less resistance to wear than the 
interior portions of the hide. The grain surface has more resist- 

Relative Loss in Weight. 



Test 1 



HI 
C2 

F3 

S-3 
FZ 
F\ 



Test 2 



F3 

FZ 
Fl 



Test 3 



GI 
62 
F3 

63 
F2 

f I 



f\veraae 



e-i 

62 

F3 

6-3 
F2 



Fig. i. — Wear resistance at different depths of a hide 

ance than the flesh side, although this difference is not so marked 
as that between the outer and inner parts. Without extensive 
researches it would be impossible to locate the specific layer 
having the greatest wearing resistance, if any such surface exists, 
which is very doubtful. 

There are several reasons to which this difference may be 
ascribed. It is probably due to a certain extent to the difference 
in the degree of tannage between the outer and the inner portions 
of the leather. The outer layers take up the tannin before the 
latter has a chance to penetrate to the interior of the hide; the 
tannins are precipitated in the surface layers and they, therefore, 
tend to retard the tanning of the central parts. In all pieces of 



Wear Resistance of Leather 5 

heavy leather the central part is probably much more lightly 
tanned than either the grain or the flesh surfaces. This may be 
clearly noticed in a piece of so-called undertanned sole leather. 
A study of the anatomy of the hide itself discloses even greater 
reasons for this wide difference in wear resistance. The part 
of the skin that goes to make up the finished leather may be 
divided into two distinct parts, the grain and the flesh, or more 
correctly speaking, the corium. The chemical constitution and 
physical structure of these two divisions are quite different. 




Fig. 2. — Grain portion. X 50 

Briefly, the grain consists of the papillary layer, of bundles of very 
fine white and elastic fibers, and it contains the sudoriferous and 
sebaceous glands. These fine fibers are clearly defined, lying 
nearly flat and extending in every direction, closely interwoven 
and overlapping, sometimes even doubling back into the lower 
fibrous layers. Fig. 2 shows a cross section of the grain portion 
of a piece of lightly rolled union sole leather magnified to 50 
diameters. The grain surface is seen as the dark portion at the 
top; beneath it may be seen the white fiber bundles with the 
glands scattered through them. 



6 Technologic Papers of the Bureau of Standards 

The corium, in Fig. 3, is composed of larger bundles or fine fibers, 
not so compactly interwoven as those of the grain portion. 

There appears to be no system in which the fiber bundles inter- 
lace themselves, but, from his extensive researches on this subject, 
Alfred Seymour- Jones has concluded that these fiber bundles are 
woven in a definite steplike manner. 1 

The flesh side of the leather, Fig. 4, consists of smaller bundles 
of fibers closely interwoven and running more nearly parallel, form- 
ing a region similar to that formed by the white fibers of the grain. 




Fig. 3. — Corium. X 50 

The grain membrane itself has very little resistance to wear. 
It deteriorates rapidly, especially in dyed leathers, and peels off 
in little flakes. Sheepskin and morocco (goat) leather show this 
defect, although it has been noted to a less extent in cow leather. 2 
The surfaces composed of the smaller bundles of fiber, although 
more compactly woven, do not possess the resistance of the larger, 
less closely knitted fiber bundles of the corium. 

1 A. Seymour- J ones, The physiology of the skin, Part XI. 

2 A. Seymour-Jones, The physiology of the skin, Part VI. 



Wear Resistance of Leather 7 

From the data obtained from this series of tests the interior 
portions of the leather appear to have a greater resistance to wear 




Fig. 4. — Flesh portion. X 50 

than either the grain or the flesh sides. There is no specific 
surface which has the greatest wear resistance. 

Washington, January 16, 1920. 



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